1. Field of the Invention
This invention relates to a gas desulfurization process utilizing a supported sorbent and to a method for the preparation of the supported sorbent. More particularly, this invention relates to the removal of acidic gases, such as hydrogen sulfide and precursors thereof, from a gaseous mixture by contacting the gaseous mixture with a regenerable sorbent comprising a steam-treated porous inorganic oxide support composited with one or more rare earth metal components.
2. Description of the Prior Art
The removal of hydrogen sulfide from gaseous streams is of primary importance to refiners. Thus, not only is hydrogen sulfide a catalyst poison for some downstream processing, e.g., methanation of carbon monoxide-containing streams, but environmental consideration dictate the removal of sulfur-containing components from fuel gases. The commercially available processes for hydrogen sulfide removal can be roughly divided into two categories, that is, low temperature processes, e.g., 200.degree.-300.degree. F. involving scrubbing the gas stream with liquid solutions such as mixtures of ethanolamines or mixtures comprising anthraquinone disulfonic acids, and high temperature processes, e.g., about 1,000.degree. F., involving contacting the gas stream with a bulk sorbent such as zinc oxide or ferric oxide.
The low temperature processes typically incorporate some regenerable compounds which also act as an oxidant, oxidizing the hydrogen sulfide to sulfur, in conjunction with a reductant, which regenerates the oxidant. The use of such processes, however, when the gaseous stream is to be combusted is disadvantageous since the gases normally produced at high temperature must be cooled before treatment for hydrogen sulfide removal. High temperature processes on the other hand lead to the formation of highly stable sulfides. Materials used in these processes can be roasted to release the sulfur as sulfur dioxide. However, roasting yields a dilute stream of sulfur dioxide (about 14%) which is costly to process if air is used as the oxygen source. More concentrated sulfur dioxide streams can be obtained by using oxygen to roast the sorbent, also a costly process. Steam may also be used but the amount of steam required is excessive. Thus, such sorbents are often discarded rather than being regenerated. Such a process is illustrated in U.S. Pat. No. 3,579,293 which discloses the use of supported ferric oxide and fly ash as the sorbent to overcome the disintegration of solid sorbents during repeated periods of burning.
It has now been found that by steam-treating a porous support prior to compositing it with a regenerable sorption active metallic component, the amount of sorption active metallic component necessary to achieve a given level of hydrogen sulfide (or precursors thereof) removal from gaseous mixtures can be significantly lowered.